1. Field of the Invention
This invention relates in general to a signal generator which has a digital memory that can digitally generate a signal such as a sine wave which has periodicity.
2. Description of the Prior Art
If a number of sample data during one period of a sine wave are stored in a memory such as a ROM and if the address of the ROM is changed step by step at predetermined intervals, a digital sine wave can be generated. The maximum value of the addresses of the ROM in this kind of digital signal generator is determined by the number of bits of the address input and the frequency of the output signal and the clock frequency, and generally this will not be (2.sup.n -1). For this reason, the address generator becomes complicated which presents a problem.
Also, another arrangement wherein a part of the data of one period of a sine wave is stored in the ROM and the data having the negative polarity is formed by inverting the polarity of the readout data from the ROM and wherein changes of the ascending and descending portion are performed by inverting the address signal. With such a construction, the capacity of the ROM can be small. For this construction, unless the number of addresses of the ROM is 2.sup.n, a complicated circuit must be used to form from the values of the address control signals for controlling the inversion of the polarity of the data read out and for controlling the ascending and descending portion of the address signal which results in the operating speed being slow.